Smoking has been suggested to be a possible risk factor for dementia. In this study the association between smoking history and cognitive decline was studied in subjects transitioning from midlife to old age.  Cognitive tests included assessment of memory, vocabulary, executive function (1 reasoning and 2 fluency tests), and a global cognitive score summarizing performance across all 5 tests. Smoking status was assessed over the entire 10 year study period and the association between smoking history and 10-year cognitive decline was analyzed.

In men, faster cognitive decline was observed among current smokers compared with never smokers. Recent ex-smokers had greater decline in executive function, while the decline in long-term ex-smokers was similar to that among never smokers. In analyses that additionally took dropout and death into account, these differences were 1.2 to 1.5 times larger. In women, cognitive decline did not vary as a function of smoking status.

The authors concluded that compared with never smokers, middle-aged male smokers experienced faster cognitive decline in global cognition and executive function. In ex-smokers with at least a 10-year cessation, there were no adverse effects on cognitive decline.

No observations were made about the effects of second-hand smoke or urban environments with heavy air pollution. These remain for future analysis.

Sabia S, Elbaz A, Dugravot A, Head J, Shipley M, Hagger-Johnson G, Kivimaki M, Singh-Manoux A: Impact of Smoking on Cognitive Decline in Early Old Age: The Whitehall II Cohort Study. Arch. Gen. Psychiatry [Epub ahead of print, Feb. 6, 2012; doi: 10.1001/archgenpsychiatry.2011.2016].

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